Since silicon materials, such as silicon (Si) and silicon oxide represented by SiOx, can intercalate more lithium ions per unit volume than carbon materials, such as graphite, use of silicon materials in negative electrodes of lithium ion batteries or other batteries has been studied. For example, Patent Literature 1 discloses a non-aqueous electrolyte secondary battery including a mixture of SiOx and graphite as a negative electrode active material.